Optical pick-up head and integrated type optical unit for use in optical pick-up head

ABSTRACT

An optical pick-up head for reading writing information from on a magneto-optical record medium including a semiconductor laser, a multi-image plane parallel plate for separating an incident light beam emitted by the semiconductor laser from a return light beam reflected by the optical record medium and dividing the return beam transmitted through and refracted by the multi-image plane parallel plate into a plurality of return light beams, and a signal detecting photodetector receiving a plurality of return light beams, wherein the multi-image plane parallel plate is formed by first and second prisms made of birefringent material and is arranged such that major and minor axes of astigmatism introduced by the plane parallel plate are inclined by 45° with respect to an information track. An optic axis of the first prism is set such that the return beam is separated into ordinary and extraordinary light beams having identical intensities and an optic axis of the second prism is rotated with respect to the optic axis of the first prism. The optical elements are positioned and mounted on a mounting substrate having guide walls formed by a photolithography.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pick-up head for use in anoptical reading and/or recording apparatus for reading and/or recordinginformation from and/or on an optical information record medium,particularly a magneto-optical record medium. The present invention alsorelates to an integrated type optical unit for use in the abovementioned optical pick-up head.

2. Related Art statement

FIG. 1 is a schematic view showing a first known optical pick-up head.The optical pick-up head reads and/or records information from and/or ona magneto-optical record medium. A linearly polarized laser beam emittedby a semiconductor laser such as a laser diode 1 is made incident upon apolarizing beam splitter 2 and a laser beam reflected by a polarizingfilm 2a provided in a contact surface between prisms is projected by anobjective lens 3 onto an information track 4a of an magneto-opticalinformation record medium 4 as a fine spot. The polarizing film 2a orthe polarizing beam splitter 2 has a transmissivity of 60-90% for acomponent vibrating in a direction perpendicular to a plane of thedrawing of FIG. 1 (S-polarized beam) and a transmissivity ofsubstantially 100% for a component vibrating in a direction parallelwith the plane of the drawing (P-polarized beam). Such a polarizing film2a may be formed by a multiple coatings of dielectric material films.The linearly polarized laser beam emitted by the semiconductor laser 1is made incident upon the polarizing film 2a as S-polarized beam.

The laser beam is reflected by the magneto-optical record medium 4 issubjected to the Kerr rotation and its polarizing direction is rotatedabout an optical axis by ±θ_(k) depending upon information recorded onthe record medium, The thus reflected return beam is converged by theobjective lens 3 and is made incident again upon the polarizing beamsplitter 2 as the converging light beam. Then, the return beam istransmitted through the polarizing film 2a so that the return beam isseparated from the incident laser beam. Then, the return beam is madeincident upon a multi-image prism 5. The multi-image prism 5 isconsisting of a first triangular prism 5a and a second triangular prism5, each being made of birefringent material. In order to detect aninformation signal recorded on the magneto-optical record medium 4 by aso-called differential method, an optic axis of the first prism 5a isset to be perpendicular to an optical axis of the return beam and to beinclined by 45° with respect to a direction perpendicular to the planeof the drawing, and an optic axis of the second prism 5b is set to beinclined by 45° with respect to the optic axis of the first primes in,for instance in the direction perpendicular to the plane of the drawing.Therefore, the return beam impinging upon the multi-image prism 5 isdivided into substantially three light fluxes. The information signalread out of the optical record medium is denoted as MO signal for sakeof simplicity.

The three light fluxes emanating from the multi-image prism 5 are thenmade incident upon a signal detecting photodetector 6 via a toric lens7. The toric lens 7 has a function for extending a focal length of thetransmitted light as well as a function as a cylindrical lens forintroducing astigmatism which is required to detect a focusing errorsignal (hereinafter the focusing error signal is called FES). Asillustrated in FIG. 2, the signal detecting photodetector 6 comprisesthree light receiving units 6a, 6b and 6c, and the middle lightreceiving unit 6b includes four light receiving regions, The MO signalis derived from a comparator 8 producing a difference between outputs ofthe light receiving units 6a and 6c, and the FES is obtained from acomparator 9 producing a difference between a sum of outputs ofdiagonally aligned light receiving regions of the light receiving unit6b and a sum of outputs of other diagonally aligned light receivingregions. A tracking error signal (denoted by TES) may be derived by, forinstance a push-pull (PP) method.

In Japanese Patent Application Laid-open Publication Kokai Hei 5-314563,there is disclosed a second known optical pick-up head, In this opticalpick-up head, in a converged return beam there is arranged a planeparallel plate having an optical anisotropy, said plane parallel platehaving a function of separating the return beam from the incident beam,a function of performing the polarizing separation for detecting the MOsignal by the differential method, and a function of introducingastigmatism for detecting the FES. Ordinary light and extraordinarylight separated by the plane parallel plate are received separately by asignal detecting photodetector.

The above mentioned first known optical pick-up head has the followingproblems:

(1) The polarizing beam splitter 2 for separating the return light pathfrom the incident light path, the multi-image prism 5 for dividing thereturn beam into a plurality of light fluxes with the aid of thepolarization, and the toric lens 7 for introducing the astigmatismrequired for detecting the FES are arranged separately from each other,and thus the optical pick-up head could not be made light in weight,small in size and cheap in cost.

(2) The semiconductor laser 1 and signal detecting photodetector 6 whichare arranged in conjugate with one another are spatially separated fromeach other by a large distance, and thus the optical pick-up head isliable to be subjected to temperature variation, secular variation, andothers, so that use of the optical head is limited by ambientconditions, In order to mitigate such a drawback, it is required to usea large and expensive housing incorporating the optical elements.

(3) An optical path length of the detecting optical system is increasedby a concave lens function of the toric lens 7, so that size of theoptical head is prolonged, although adjustment of the signal detectingphotodetector 6 becomes easy.

In the second known optical pick-up head, the plane parallel platehaving optical anisotropy has all the three functions, i.e. separatingthe return beam from the incident beam, polarizing beam splittingfunction and astigmatism introducing function, the above mentionedproblems (2) and (3) of the first known optical pick-up head can bemitigated. However, the second known optical pick-up head has thefollowing problems:

(4) A direction in which the astigmatism for detecting the FES isintroduced is in parallel with a track direction in which an informationtrack extends or is perpendicular to the track direction. Therefore, apush-pull signal for detecting the tracking error is leaked into the FESand the focusing servo is liable to be unstable.

(5) The FES is detected only from one of the polarizing split beams, andthus an amplitude of the FES fluctuates due to a birefingency of asubstrate of the magneto-optical record medium and an accurate focusservo control could not be performed,

(6) A positioning of the signal detecting photodetector is difficult,

(7) In the first known optical pick-up head shown in FIGS. 1 and 2, thenumber of optical elements is large, so that a total error representedby a sum of errors of respective optical elements becomes very large. Inorder to absorb these errors, the photodetector 6 has to be adjusted inxyz axes or the photodetector has to be adjusted in xy axes and thetoric lens 7 has to be adjusted in z axis. In this manner, it isrequired to perform a very cumbersome three axis adjustment. In thiscase, the xy axis adjustment could not be independent from the z axisadjustment, so that a number of adjusting steps are increased.

(8) Moreover, since the number of optical elements provided within aportion 10 surrounded by a chain line in FIG. 1 is large, an actual sizeof the portion 10 amounts to several tens to several hundredsmillimeters by considering a space for providing adjusting mechanisms.Therefore, it is required an expensive housing consisting of a severalblocks and complicated workings are required in order to manufacturethese blocks.

In known optical pick-up heads, a housing for accommodating the opticalelements is manufactured by a mechanical process by using lathe, millerand NC lathe, and then the optical elements are fixed to the housing bymeans of screws and adhesive agent, Therefore, the housing is liable tobecome large and moreover positioning errors of the optical elementscould be hardly limited to micron order.

In Japanese Patent Application Laid-open Publications Kokai Sho62-197931 and 62-283430, there is disclosed a third known opticalpick-up head. In this optical pick-up head, on a semiconductor substratehaving photo diodes formed therein there are provided a beam splitterand a laser diode to constitute a single integrated body. This opticalpick-up head can reduce a cost and a size. Moreover, in Japanese PatentApplication Laid-open Publication Kokai Hei 3-44086, there is proposed alaser unit for use in the optical pick-up head. In this laser unit, alaser diode is sealed within a housing in which a collimator lens isprovided.

If the above mentioned third known optical pickup head in applied to aninfinite optical system using the collimator lens, it is necessary toadjust positions of a substrate on which the beam splitter and laserdiode are secured with respect to an optical axis of the collimatorlens, and this requires an adjusting mechanism and fixing parts thereforas well as spaces for the these elements. In this manner, although thebeam splitter and laser diode are secured to the substrate in which thephoto diodes are formed, size and cost of the optical pick-up head couldnot be reduced sufficiently.

In the laser unit described in the above mentioned Japanese PatentApplication Laid-open Publication Kokai Hei 3-44086, the collimator lensis secured to the housing in such a manner that an outer periphery ofthe collimator lens is cemented to an inner wall of a circular openingformed in the housing. Therefore, the collimator lens could not be movedin a direction perpendicular to the optical axis of the laser diode, sothat an adjustment of a propagating direction of a collimated beam islimited. Further, in this laser unit, a distance between the laser diodeand the collimator lens could not be determined accurately, so that anaccurately collimated laser beam has to be obtained by changing anoscillation frequency of the laser diode by adjusting an injectioncurrent therefor. Therefore, the laser unit could not be applied to anoptical pick-up head in which a power of the laser beam is changedbetween the reading and the recording by adjusting the injection currentto the laser diode. Moreover, the semiconductor laser whose wavelengthis varied in accordance with the Injection current could not bemanufactured at a large scale at present and is expensive.

SUMMARY OF THE INVENTION

The present invention has for its object to provide a novel and usefuloptical pick-up head, which can be small in size, light in weight andcheap in coot and can derive an accurate focusing error signal so that afocusing control can be performed precisely.

It is another object of the invention to provide a novel and usefulintegrated type optical unit for use in an optical pick-up head, whichcan be small in size, light in weight and cheap in cost, can provide aneasy and accurate adjustment and positioning of optical elements, andcan endeavor ambient conditions.

It is another object of the invention to provide an integrated typeoptical unit, in which an adjustment of an collimator lens in adirection of its optical axis can be dispensed with, so that the opticalunit can be small in size and cheap in cost.

It is another object of the invention to provide an integrated typeoptical unit, in which an optical axis of a collimated beam can beperformed by means of a collimator lens.

It is another object of the invention to provide an integrated typeoptical unit which can be small in size and cheap in cost and improve areliability.

According to the invention, an optical pick-up head for reading and/orrecording information from and/or on a magneto-optical record mediumcomprises:

a semiconductor laser emitting a linearly polarized light flux;

an objective lens projecting said light flux onto a magneto-opticalrecord medium as a fine spot;

a multi-image plane parallel plate arranged between said semiconductorlaser and the objective lens in a converged return light flux reflectedby said record medium, reflecting the linearly polarized light fluxemitted by said semiconductor laser toward said objective lens andtransmitting and refracting said return light flux to introduceastigmatism in the return light flux and to perform a polarizing beamsplitting, said multi-image plane parallel plate including a firsttriangular prism and a second triangular prism which are made ofbirefringent material and are joined with each other; and

a signal detecting photodetector receiving a plurality of light fluxesemanating from said multi-image plane parallel plate, detecting aninformation signal from outputs corresponding to mutually orthogonallypolarized light components, and detecting a focusing error signal fromoutputs corresponding to ordinary and extraordinary light components;wherein said multi-image plane parallel plate is arranged such thatdirections of major and minor axes of said astigmatism are inclined by45 degrees with respect to a track direction in which an informationtrack on the magneto-optical record medium extends, an optic axis ofsaid first triangular prism is set such that said return light flux isdivided into the ordinary light and extraordinary light havingsubstantially identical intensities, a polarizing film is provided on asurface of the first triangular prism upon which said linearly polarizedlight flux and return light beam are made incident, and an optic axis ofsaid second triangular prism is set to be inclined by a predeterminedangle with respect to the optic axis of the first triangular prism.

In a preferable embodiment of the optical pick-up head according to theinvention, said semiconductor laser is arranged such that a light spotformed by the objective lens on the magneto-optical record mediumbecomes an elliptical shape whose major axis is inclined by 45° withrespect to the information track, and a half wavelength plate isarranged between the polarizing film and the objective lens such that apolarizing direction of the linearly polarized light flux emitted by thesemiconductor laser and impinging upon the record medium becomes inparallel with the information track. Then, an amplitude of a trackingerror signal obtained by the push-pull method can be maximized.

In another preferable embodiment of the optical pick-up head accordingto the invention, said semiconductor laser is arranged such that a lightspot formed by the objective lens on the magneto-optical record mediumbecomes an elliptical shape whose major axis is perpendicular to theinformation track, and a first half wavelength plate is arranged betweenthe semiconductor laser and the polarizing film and a second halfwavelength plate is arranged between the polarizing film and theobjective lens such that a polarizing direction of the linearlypolarized light flux emitted by the semiconductor laser and impingingupon the record medium become in parallel with the information track. Insuch an embodiment, a high resolution can be attained and the push-pullsignal having a large amplitude can be obtained.

Now it is assumed that an angle between the optic axis of the firsttriangular prism and the optic axis of the second triangular prismmeasured about the optical axis of the return beam is β. In a preferableembodiment of the optical pick-up head according to the invention, saidangle β is set to 45°≦β(≠90°)≦135°, said return beam is divided into afirst light beam containing both the ordinary and extraordinary lightcomponents of substantially identical intensities, and second and thirdlight beams having polarizing directions which are perpendicular to eachother, said signal detecting photodetector comprises a first lightreceiving unit having four light receiving regions receiving said firstlight beam containing both the ordinary and extraordinary lightcomponents and second and third light receiving units receiving saidsecond and third light beams, respectively. Then, the FES is detectedfrom a difference between a sum of outputs of orthogonally aligned lightreceiving regions of the first light receiving unit and a sum of outputsof a second set of orthogonally aligned light receiving regions of thefirst light receiving unit, and the MO signal is obtained from adifference between outputs of said second and third light receivingunits. In this embodiment, it is possible to obtain the FES accuratelyand the MO signal has improved S/N.

In a preferable embodiment of the optical pick-up head according to theinvention, said angle β is set to 90°, the return beam is divided intofirst and second light beams having polarizing directions which areperpendicular to each other emanate from the multi-image plane parallelplate separately from each other, said signal detecting photodetectorcomprises first and second light receiving units each having four lightreceiving regions receiving respective one of said orthogonallypolarized first and second light beams. Then, the MO signal is obtainedfrom a difference between a sum of the four light receiving regions ofthe first light receiving unit and a sum of the four light receivingregions of the second light receiving unit and the FES is detected froma sum of a first difference between a sum of outputs of orthogonallyaligned light receiving regions of the first light receiving unit and asum of outputs of a second set of orthogonally aligned light receivingregions of the first light receiving unit, and a second differencebetween a sum of orthogonally aligned light receiving regions and a sumof orthogonally aligned light receiving regions of the second lightreceiving unit. Then, the MO signal having a good S/N can be obtainedand the FES can be derived accurately although the signal detectingphotodetector can be small in size.

As explained above, in the optical pick-up head according to theinvention, the linearly polarized laser beam emitted by thesemiconductor laser is reflected by the polarizing film applied on thesurface of the multi-image plane parallel plate and then is projectedonto the magneto-optical record medium as the fine light spot. Thereturn beam reflected by the record medium is made incident upon themulti-image plane parallel plate by means of the objective lens and isseparated from the incident light beam. The return beam is subjected tothe polarizing beam splitting function as well as the astigmatism suchthat the directions of the major and minor axes of the astigmatism areset to be inclined by about 45° with respect to the information track ofthe record medium. The return beams thus divided and being subjected tothe astigmatism are received by the photodetector. The MO signal isderived from the outputs of the photodetector corresponding to themutually orthogonally polarized components and the FES can be obtainedfrom the outputs corresponding to the ordinary and extraordinary lightcomponents having substantially identical intensities.

According to the invention, an integrated type optical unit for use inan optical pick-up head for reading and/or recording information fromand/or on an optical record medium by projecting a light flux emittedfrom a semiconductor laser onto an optical record medium and byreceiving a return beam reflected by the optical record medium by meansof a signal detecting photodetector, wherein said semiconductor laser,signal detecting photodetector and a light path separating element fordirecting the light beam emitted by the semiconductor laser toward theoptical record medium and directing the return beam reflected by theoptical record medium toward the photodetector are positioned on amounting substrate including positioning guides formed by aphotolithography.

According to the invention, said substrate is preferably formed by asingle crystal silicon wafer, so that the highly precise positioningguides can be formed.

In a preferable embodiment of the optical unit according to theinvention, a monitoring photodetector for monitoring an amount of lightemitted by said semiconductor laser is provided by positioning with apositioning guide. Then, an output power of the semiconductor laser canbe controlled in accordance with an output of the monitoringphotodetector.

In a preferable embodiment of the optical unit according to theinvention, Raid light path separating element is formed by a multi-imageplane parallel plate including first and second triangular prisms madeof birefringent materials and joined together, whereby an optic axis ofsaid first triangular prism is set such that said return light flux isdivided into ordinary light and extraordinary light having substantiallyidentical intensities, a polarizing film is provided on a surface of thefirst triangular prism upon which said light flux emitted by thesemiconductor laser and return light beam are made incident, and anoptic axis of said second triangular prism is set to be inclined by apredetermined angle with respect to the optic axis of the firsttriangular prism. In this embodiment, it is possible to obtain the MOsignal having high S/N and the FES in a precise manner.

In a preferable embodiment of the optical unit according to theinvention, said mounting substrate comprises an upper substrate and alower substrate each being made of silicon single crystal, recesses areformed In the lower substrate by anisotropic etching and correspondingopenings are formed in the upper substrate by anisotropic etching, saidupper and lower substrates being joined together to constitute thepositioning guides by said recesses and openings. In this embodiment,the recess and opening can define positioning surfaces for differentdirections, so that a desired element can be easily and positivelyarranged in position.

According to the invention, an integrated type optical unit for use inan optical pick-up head for reading and/or recording information fromand/or on an optical record medium comprises: a mounting substrateincluding a silicon wafer having a (110) uppermost surface and havingformed therein upright recesses or upright walls each formed by (111)surfaces;

a semiconductor laser secured to one or more upright recesses or uprightwalls, positioned at least in a direction of an optical axis of thesemiconductor laser and emitting a light beam;

a photodetector secured to one or more upright recesses or uprightwalls, positioned at least in a direction of an optical axis or thephotodetector and receiving a return beam reflected by an optical recordmedium; and

an optical path separating element secured to one or more uprightrecesses or upright walls, positioned at least in a direction of anoptical axis thereof, directing the light beam emitted by thesemiconductor laser toward the optical record medium and directing thereturn beam toward the photodetector.

According to the invention, an integrated type optical unit for use inan optical pick-up head for reading and/or recording information fromand/or on an optical record medium comprises:

a mounting substrate including a silicon wafer having a (100) uppermostsurface and having formed therein a plurality of pyramid recesses with{111} side walls;

a semiconductor laser secured to A pyramid recess of the mountingsubstrate, positioned at least in a direction of an optical axis of thesemiconductor laser and emitting a light beam;

a photodetector secured to a pyramid recess, positioned at least in adirection of an optical axis of the photodetector and receiving a returnbeam reflected by an optical record medium; and

an optical path separating element secured to a pyramid recess,positioned at least in a direction of an optical axis thereof, directingthe light beam emitted by the semiconductor laser toward the opticalrecord medium and directing the return beam toward the photodetector.

According to the invention, an integrated type optical unit for use inan optical pick-up head for reading and/or recording information fromand/or on an optical record medium comprises:

a mounting substrate including an uppermost polyimide film having aplurality of upright recesses;

a semiconductor laser secured to one of said upright recesses of themounting substrate, positioned at least in a direction of an opticalaxis of the semiconductor laser and emitting a light beam;

a photodetector secured to another one of said upright recesses of themounting substrate, positioned at least in a direction of an opticalaxis of the photodetector and receiving a return beam reflected by theoptical record medium; and

an optical path separating element secured to another one of saidupright recesses of the mounting substrate, positioned at least in adirection of an optical axis of the optical path separating element,directing the light beam emitted by the semiconductor laser toward theoptical record medium and directing the return beam reflected by theoptical record medium toward the photodetector.

According to further aspect of the invention, an integrated type opticalunit for use in an optical pick-up head for reading and/or recordinginformation from and/or on an optical record medium comprises:

a mounting substrate including a silicon wafer having a (110) uppermostsurface and having formed therein a plurality of upright walls formed by{111} surfaces;

a semiconductor laser secured to one or more (111) upright walls andemitting a light beam;

a photodetector secured to one or more (111) upright walls differentfrom said one or more upright walls to which said semiconductor laser issecured, and receiving a return beam reflected by the optical recordmedium; and

an optical path separating element secured to at least two convexcorners of upright walls different from the upright walls to which saidsemiconductor laser and photodetector are secured, a rotation of saidoptical path separating element being inhibited by said at least twoupright walls, directing the light beam emitted by the semiconductorlaser toward the optical record medium and directing the return beamreflected by the optical record medium toward the photodetector.

In a preferable embodiment of the optical unit according to theinvention just mentioned above, the upright walls to which thesemiconductor laser is secured and the upright walls to which thephotodetector is secured are formed by (111) surfaces having the sameorientation. In such an embodiment, desired distances between thesemiconductor laser, photodetector and optical path separating elementcan be attained with a precision of micron order.

In order to adjust the positioning for the semiconductor laser andphotodetector easily and accurately, it in preferable to form airconduit holes in the mounting substrate. In this case, the semiconductorlaser and photodetector can be urged against the upright walls bysucking an air through the air conduit holes,

In the optical unit according to the invention, said upright walls canbe formed in the mounting substrate with an extremely high precision byusing light reducing method and anisotropic etching which have beenhighly developed in a semiconductor manufacturing field. Therefore, theoptical elements can be positioned accurately with a precision of micronorder. Moreover, the optical unit can be small in size, light in weightand thin in thickness, and further the optical unit can be used undersever conditions.

According to further aspect of the invention, an optical pick-up headfor reading and/or recording information from and/or on an opticalrecord medium, in which a laser beam emitted by a laser diode isreflected by a beam splitter and then is made incident upon an opticalrecord medium by means of a collimator lens and an objective lens as afine spot, a return laser beam reflected by the optical record mediumis-made incident upon the beam splitter via the objective lens andcollimator lens, and the return laser beam transmitted through andrefracted by the beam splitter is made incident upon a photodetector,wherein the improvement comprises a block including a mounting substrateon which the laser diode, beam splitter and photodetector are mounted, abase member on which said block and collimator lens are mounted, areference surface formed in said block perpendicular to an optical axisof a light flux emanating from said mounting substrate, an abutmentsurface formed in said base member, against which said reference surfaceis urged, and a fixing surface amounting said collimator lens, saidsecuring surface being parallel with said abutment surface.

In this optical pick-up head, the abutment surface formed in the basemember and the collimator lens securing surface are made in parallelwith each other, so that a distance between these surfaces can beprecisely determined by machine working and thus the adjustment of thecollimator lens in a direction of its optical axis can be dispensedwith.

According to further aspect of the invention, an optical pick-up headfor reading and/or recording information from and/or on an opticalrecord medium, in which a laser beam emitted by a laser diode isreflected by a beam splitter and then in made incident upon an opticalrecord medium by means of a collimator lens and an objective lens as afine spot, a return laser beam reflected by the optical record medium ismade incident upon the beam splitter via the objective lens andcollimator lens, and the return laser beat transmitted through andrefracted by the beam splitter is made incident upon a photodetector,wherein the improvement comprises a block including A mounting substrateon which the laser diode, beam splitter and photodetector are mounted, abase member on which said block and collimator lens are mounted, and aflat mounting surface formed in said base member for mounting saidcollimator lens, whereby said collimator lens has a flat surface whichis parallel with said flat mounting surface and the collimator lens ismounted on the base member such that said flat surface is urged againstsaid flat mounting surface of the base member.

In this optical pick-up head, the collimator lens is mounted on the flatsecuring surface formed in the base member, and therefore the collimatorlens can be adjusted in a plane perpendicular to its optical axis.

In a preferable embodiment of the optical pick-up head according to theinvention, said block is closed by means of the collimator lens, basemember and cover member. In this case, the optical elements arrangedwithin the closed space of the block can be effectively prevented frombeing degraded by moisture, dust and electrical influence, so that it ispossible to realize an optical pick-up head having a high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a known optical pick-up head;

FIG. 2 is a schematic view illustrating a photodetector shown in FIG. 1;

FIG. 3 is a schematic view depicting a first embodiment of the opticalpick-up head according to the invention;

FIG. 4 is a schematic view of a multi-image plate shown in FIG. 3;

FIG. 5 is a diagram explaining the function of the multi-image plate;

FIG. 6 is a schematic view of a photodetector shown in FIG. 3;

FIG. 7 is a schematic view illustrating a first modification of theembodiment shown in FIG. 3;

FIG. 8 is a schematic view depicting a second modification of theembodiment of FIG. 3;

FIG. 9 is a schematic view showing a third modification of theembodiment illustrated in FIG. 3;

FIG. 10 is a diagram representing a function of a multi-image plate ofthe embodiment shown in FIG. 9;

FIG. 11 is a schematic view illustrating a positional relationship ofoptical elements in the first embodiment shown in FIG. 3;

FIG. 12 is a cross sectional view showing a second embodiment of theoptical pick-up head according to the invention;

FIG. 13 is a perspective cross sectional view explaining an etchingprocess forming a mounting substrate shown in FIG. 12;

FIGS. 14A, 14B and 14C are schematic views illustrating a thirdembodiment of the optical pick-up head according to the invention;

FIG. 15 is a schematic view depicting a basic optical construction of afourth embodiment of the optical pick-up head according to theinvention;

FIG. 16 is a schematic view showing the whole construction of the fourthembodiment;

FIG. 17 is a schematic plan view of a photodetector shown in FIG. 16;

FIGS. 18A and 18B are side and plan views, respectively illustrating anoptical unit of a fifth embodiment of the optical pick-up head accordingto the invention;

FIGS. 19A, 19B, 20A, 20B and 21A, 21B are schematic view explaining theanisotropic etching forming a mounting substrate;

FIG. 22 is a schematic view representing an optical unit of a sixthembodiment of the optical pick-up head according to the invention;

FIGS. 23A, 23B and 23C are schematic views illustrating mountingrecesses;

FIGS. 24A, 24B and 24C are schematic views showing an optical unit of aseventh embodiment of the optical pick-up head according to theinvention;

FIGS. 25A and 25B are schematic view depicting a manner of mounting abeam splitting element shown in FIG. 24B;

FIGS. 26A, 26B and 26C are schematic views explaining another method ofmounting the beam splitting element;

FIGS. 27A, 27B and 27C show a manner of mounting optical elements on amounting substrate;

FIGS. 28A, 28B, 28C, 28D, 28E and 28F are schematic views showing amounting substrate of an eighth embodiment of the optical pick-up headaccording to the invention;

FIGS. 29A, 29B and 29C are schematic views showing a mounting substrateof a ninth embodiment of the optical pick-up head according to theinvention;

FIG. 30 is a schematic view depicting an optical unit of a tenthembodiment of the optical pickup head according to the invention;

FIG. 31 is a schematic view illustrating a part of an optical unit of aneleventh embodiment of the optical pick-up head according to theinvention;

FIG. 32 is a cross sectional view showing an air suction holes;

FIGS. 33A, 33B and 34A, 34B are schematic views explaining theanisotropic etching;

FIG. 35 is a schematic view representing a modification of the tenthembodiment;

FIGS. 36A and 36B are schematic views illustrating a twelfth embodimentof the optical pick-up head according to the invention;

FIGS. 37A and 37B are schematic views depicting an optical unit of thetwelfth embodiment;

FIGS. 38A and 38B are schematic views showing a thirteenth embodiment ofthe optical pick-up head according to the invention;

FIGS. 39A and 39B are schematic views illustrating an optical unit ofthe thirteenth embodiment; and

FIGS. 40A and 40B are schematic views showing an optical unit of afourteenth embodiment of the optical pick-up head according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a schematic view illustrating a first embodiment of theoptical pick-up head according to the invention. In the presentembodiment, a linearly polarized diverging light beam emitted by asemiconductor laser 11 is made incident upon a multi-image planeparallel plate 12 having a polarizing film 13 applied on an incidentsurface. A light flux transmitted through the polarizing film 13 andmulti-image plane parallel plate 12 is received a monitor photodetector14 and an output power of the semiconductor laser 11 is controlled inaccordance with an output of the monitor photodetector 14.

A light beam reflected by the polarizing film 13 is made incident upon a45° rotator 15 so that a polarizing direction of the linearly polarizedlight beam is rotated by 45°. The light beam emanating from the rotator15 is projected by an objective lens 16 upon a magneto-optical recordmedium 17 as a very fine spot. A return light beam reflected by themagneto-optical record medium 17 is converged by the objective lens 16and is made incident upon the polarizing film 13 via the 45° rotator 15.Then, the return light beam is separated from the incident light beam bythe polarizing film 13 and is transmitted and refracted by themulti-image plane parallel plate 12, so that astigmatism is introducedinto the return beam and the return beam is divided into a plurality oflight beams by the polarizing beam splitting function. The thus dividedlight beams are received by a photodetector 18 to derive MO signal, FESand TES.

The semiconductor laser 11 is arranged in such an orientation that adirection of the polarization of the linearly polarized laser beamemitted by the semiconductor laser is not such that the laser beam inmade incident upon the polarizing film 13 as S-polarized beam. Themulti-image plane parallel plate 12 is arranged such that a major axisand a minor axis of the astigmatism introduced by the plate 12 into thereturn light beam are inclined by 45° with respect to an informationtrack 17a on the magneto-optical record medium 17. The plane parallelplate 12 is formed by first and second triangular prisms 19 and 20 madeof lithium niobate, said first and second prisms being joined with eachother. The polarizing film 13 is applied on an incident surface of thefirst prism 19, upon which the diverging light beam emitted by thesemiconductor laser 11 as well as the return light beam reflected by themagneto-optical record medium 17 are made incident. The polarizing film13 is formed by multi-coatings of dielectric films such that S-polarizedlight vibrating perpendicularly to a plane of the drawing of FIG. 3 isreflected by 60-90% but P-polarized light vibrating in the plane of thedrawing of FIG. 3 is transmitted by 100%.

The light beam emitted by the semiconductor laser 11 has an ellipticalcross section, so that if there is not adopted any beam shaping, a lightspot formed on the magneto-optical record medium 17 becomes alsoelliptical. Since the multi-image plane parallel plate 12 is inclined by45° in the plane perpendicular to the plane of the drawing, and thusmajor and minor axes of the elliptical spot are inclined by 45° withrespect to a track direction in which the information track 17a extends.Therefore, the polarizing direction might be inclined by 45° withrespect to the information track 17a. In the present embodiment, thepolarizing direction of the incident light beam is rotated by 45° bymeans of the rotator 15, so that the polarizing direction of theincident light beam is parallel with the track direction, In thismanner, it is possible to attain the push-pull (PP) signal having amaximum amplitude.

The 45° rotator 15 is made of quartz out in a z-x or z-y plane and ispolished to have such a thickness that ordinary light and extraordinarylight have a relative phase difference of 180°. Such a rotator is alsocalled a quarter wavelength plate. The 45° rotator 15 may be made ofquartz cut in z axis cross section and is polished to have such athickness that right-handed circularly polarized beam and left-handedcircularly polarized beam have a phase difference of 90°. The latterrotator is not depends on the polarizing direction of the linearlypolarized beam.

FIG. 4 is a schematic view showing the multi-image plane parallel plate12 of the present embodiment. The first and second triangular prisms 19and 20 have an apex angle α smaller than 45°. In order to divide thereturn beam into ordinary and extraordinary light beams havingsubstantially equal intensities, an optic axis of the first prism 19 isset to be perpendicular to an optical axis of the return beam and isinclined by 45° with respect to the plane perpendicular to a plane ofthe drawing of FIG. 4. An optic axis of the second prism 20 is rotatedby β with respect to the optic axis of the first prism 19 viewed in theplane perpendicular to the optical axis. In the present embodiment, β isset to 45°.

By setting the optic axes of the first and second prisms 19 and 20 inthe manner explained above, the return beam is first divided by thefirst prism 19 into ordinary light O and extraordinary light E havingsubstantially identical intensities as depicted in FIG. 5. Then, theordinary light O is divided by the second prism 20 into ordinary lightOO and extraordinary light OE and similarly the extraordinary light E isdivided by the second prism 20 into ordinary light EO and extraordinarylight EE. In this manner, the return beam impinging upon the multi-imageplane parallel plate 12 is divided into the four beams OO, OE, EO and EEby the polarizing beam splitting function. In this case, propagatingdirections of the ordinary light OO and extraordinary light EE aresubstantially coincided with each other, so that there are emanatedthree light beams from the multi-image plane parallel plate 12.

In FIG. 3, the signal detection photodetector 18 is arranged such thatits light receiving plane situates at a best image plane of theastigmatism introduced by the plane parallel plate 12. FIG. 6 is a planview of this photodetector 18. The photodetector 18 comprises a firstlight receiving unit 21 receiving the light beam EO, a second lightreceiving unit 22 receiving the light beam OE and a third lightreceiving unit 23 including four light receiving regions receiving thelight beams OO and BE.

Then, the light receiving units 21 and 22 receive the light beamspolarized in mutually orthogonal directions, and thus the MO signal canbe derived by a difference between outputs of these light receivingunits 21 and 22, Further, the FES can be obtained by deriving adifference between a first sum of outputs of a first pair oforthogonally aligned light receiving regions and a second sum of outputsof outputs of a second pair of orthogonally aligned light receivingelements of the light receiving unit 23. In FIG. 3, an optical unit 24encircled by a dot and dash line is shown on the same plane on which theremaining optical elements are shown, but in practice the optical unit24 is inclined by 45° about the z axis. That is, x' and y' axes shown inFIG. 3 are inclined by 45° with respect to the x and y axes. Therefore,the image of the information track 17a on the light receiving unit 23extends in the x axis along which the light receiving regions aredivided. Then, the TES can be obtained by deriving a difference betweena third sum of outputs of a third pair of light receiving regionsarranged on one side of the x axis and a fourth sum of outputs of afourth pair of light receiving regions arranged on the other side of thex axis by the PP method.

In the present embodiment, Since the image of the information track 17aon the light receiving unit 23 is aligned with the x axis along whichthe light receiving regions are divided, it is possible to preventinfluence of the PP signal upon the FES, and at the same time the twolight beams polarized in the mutually orthogonal directions and havingsubstantially equal intensities are made incident upon this lightreceiving unit 23, influence due to a birefringency of a substrate ofthe magneto-optical record medium 17, and thus it is possible to detectthe FES with high precision and sensitivity.

Moreover, the multi-image plane parallel plate 12 is made of lithiumniobate having a birefringency, and thus a distance between themulti-image plane parallel plate 12 and the signal detectionphotodetector 18 can be 1-2 mm without providing a concave lens, so thatthe return bean can be positively divided by the polarizing beamsplitting function. Therefore, the optical pick-up head according to theinvention can be small in size and thin in thickness, When the quartz isused as the birefringent crystal, since a difference in a ratio betweenan index of refraction n_(o) for ordinary light and an index ofrefraction n_(e) for extraordinary light is about 0.6%, it is impossibleto attain a sufficiently long optical path length necessary forseparating the light beams from each other. However, when use is made oflithium niobate having n_(o) =2.286 and n_(e) =2.2, a difference in aratio between n_(o) and n_(e) is about 4%. Therefore, the light beamscan be positively separated from each other even If a distance betweenthe multi-image plane parallel place 12 and the photodetector 18 isshort such as 1-2 mm.

In the first embodiment, a finite optical system is adopted, butaccording to the invention an infinite optical system can be alsoadopted. In this case, a collimator lens is arranged between themulti-image plane parallel plate 12 and the objective lens 16 so thatthe multi-image plane parallel plate is located in a converging opticalpath of the return beam. In the present embodiment, the polarizing film13 is directly applied on the incident surface of the first triangularprism 19, but according to the invention, a plane parallel glass platemay be arranged in front of the incident surface of the first prism andthe polarizing film may be applied on this plane parallel glass plate.In this case, the polarizing film 13 may be easily designed.

According to the invention, the optic axes of the first and secondtriangular prisms 19 and 20 constituting the multi-image plane parallelplate 12 may be set at will in accordance with birefringent materials tobe used. In the above mentioned first embodiment, the optic axes of thefirst and second triangular prisms 19 and 20 are set to form an angleβ=45° viewed about the optical axis in the plane perpendicular to theoptical axis of the return beam, and therefore the a ratio ofintensities of the light beams EO, OE and (OO+EE) becomes 1:1:2.According to the invention, said angle β may be set to 45°<β(≠90)<135°.Then, OO=EE<OE=EO and an amount of a light beam impinging upon the lightreceiving units 21 and 22 is increased so that S/N of the MO signal canbe improved.

The multi-image plane parallel plate 12 may be made of birefringentmaterials other than lithium niobate. For instance, KDP and ADP may beutilized. KDP has n_(o) =1.51 and n_(e) =1.47 and ADP has n_(o) =1.52and n_(e) =1.48, so that a difference in ratio of n_(o) and n_(e) ofthese materials is equal to or more than 2%. Therefore, thesebirefringent materials can be advantageously utilized to form themulti-image plane parallel plate 12, and the light beams emanating fromthe multi-image plane parallel plate can be positively separated fromeach other without provided a concave lens between the multi-image planeparallel plate 12 and the photodetector 18 and a distance between theseelements can be made short such as 1-2 mm. Therefore, the opticalpick-up head can be made small in size and thin in thickness.

In a first modification of the first embodiment of the optical pick-uphead according to the invention, the 45° rotator 15 in the firstembodiment is dispensed with and the linearly polarizing direction andthe major and minor axes of the elliptical laser beam spot formed on themagneto-optical record medium are inclined by 45° with respect to theinformation track 17a as illustrated in FIG. 7. In this modification, anamplitude of the PP signal is slightly decreased, but the number ofparts can be reduced, so that the optical pick-up head can be small insize, light in weight and cheap in cost.

In a second modification of the optical pick-up head according to theinvention, the semiconductor laser 11 is rotated by 45° about theoptical axis, a 45° rotator is arranged between the semiconductor laser11 and the multi-image plane parallel plate 12 such that the linearlypolarized laser beam emitted by the semiconductor laser 11 is madeincident upon the polarizing film 13 as S-polarized beam, and a lightspot is formed on the magneto-optical record medium 17 such that thepolarizing direction and the minor axis of the elliptical beam are inparallel with the information track 17a as depicted in FIG. 8.

In this second modification, it is possible to attain similar advantagesto those of the first embodiment and further a resolution can beincreased, because a size of the beam spot in the track direction can bereduced. Moreover, the 45° rotator arranged between the semiconductorlaser 11 and the multi-image plane parallel plate 12 can be identicalwith the 45° rotator 15 arranged between the multi-image plane parallelplate 12 and the objective lens 16, so that rotators of a single kindcan be commonly used as both the rotators.

FIG. 9 shows a photodetector of a third modification of the firstembodiment. In this third modification, the angle β between the opticaxes of the first and second triangular prisms 19 and 20 about theoptical axis is set to 90°, and a signal detecting photodetector 18'comprises two light receiving units 21' and 22' each including fourlight receiving regions. When β=90°, the multi-image plane parallelplate 12 becomes a Wollaston's prism and an intensity of light beams(OO+EE) becomes zero, so that only two light beams OE and EO emanatefrom the multi-image plane parallel plate 12, said light beams beingpolarized in mutually orthogonal directions.

In the third modification, the light beam EO is received by the lightreceiving unit 21' and the light beam OE is received by the lightreceiving unit 22'. Then, the MO signal can be derived as a differencebetween a first sum of outputs of the light receiving unit 21' and asecond sum of outputs of the light receiving unit 22', and the FES canbe obtained by a sum of a first difference between outputs of a firstpair of light receiving regions aligned diagonally and outputs of asecond pair of light receiving regions aligned diagonally of the lightreceiving unit 21' and a second difference between outputs of a firstpair of light receiving regions aligned diagonally and outputs of asecond pair of light receiving regions aligned diagonally of the lightreceiving unit 22'. It should be noted that the TES may be detected bythe PP method like as the first embodiment.

In a fourth modification of the first embodiment of the optical pick-uphead according to the invention, a grating is arranged between thesemiconductor laser 11 and the multi-image plane parallel plate 12 andthe light beam emitted by the semiconductor laser 11 is divided into amain beam and two sub-beams, and these three beams are made incidentupon the magneto-optical record medium 17 such that they have apredetermined relationship with respect to the information track 17a.There are provided light receiving units receiving return beams of thetwo sub-beams, while a return beam of the main beam is received in asimilar manner to that of the first embodiment to derive the MO signaland FES. Then, the FES is detected by the three-beam method by receivingthe two sub-return beams by the added light receiving units.

Now several embodiments of the integrated type optical unit for use inthe optical pick-up head according to the invention will be explained.

The optical pick-up head according to the invention may be realized asthe infinite optical system or finite optical system. In an actualexample of the infinite optical system without the beam shapingfunction, the collimator lens or in an actual example of the finiteoptical system without the beam shaping function, NA of the objectivelens on a side of the semiconductor laser 11 is 0.15 and NA on a side ofthe record medium 17 is 0.55, so that a magnification is about 3.7. Withthe beam shaping function, NA of the collimator lens becomes smallerthan the above mentioned values, so that the magnification is furtherincreased.

In such an optical system, when a focal depth at the record medium hasto be set to ±1 μm, a movement of the image on the signal detectingphotodetector in the direction of the optical axis becomes ±μm×2×3.7²┤±27 μm. It is practically impossible to adjust the photodetector in thex, y and z axes within said value. Therefore, in the known opticalpick-up head, a concave lens is provided to increase a magnification anda positioning precision in enlarged, so that the adjustment of thephotodetector in the direction of the optical axis is performed.However, it is undesired to provide the concave lens in order to makethe optical head small in size and thin in thickness.

Moreover, if the adjustment of the signal detecting photodetector incarried out only in two axes in a plane, it is required to adjust thephotodetector in the optical axis with respect to an imaginary conjugatepoint of a light emitting point of the semiconductor laser. Furthermore,in this case, it is impossible to absorb other errors in the directionof the optical axis by the adjustment, so that the following errors haveto be not larger than ±10 μm by considering a fluctuation in a normaldistributions (1) error in positioning the semiconductor laser in thedirection of the optical axis; (2) error in a thickness of themulti-image plane parallel plate; (3) error in positioning themulti-image plane parallel plate; (4) error in positioning the signaldetecting photodetector; and (5) other errors.

FIG. 11 is a schematic view illustrating a positional relationship ofthe semiconductor laser 11, signal detecting photodetector 18 andmulti-image plane parallel plate 12 for separating the incident lightbeam and return light beam from each other, Now it is assumed that adistance from the semiconductor laser 11 to the polarizing film 13 is a,a distance from the polarizing film 13 to the signal detectingphotodetector 18 via the multi-image plane parallel plate 12 is b+c andan index of refraction of the multi-image plane parallel plate 12 is n.Then, an optical conjugate positional relationship of the semiconductorlaser 11, multi-image plane parallel plate 12 and photodetector 18becomes a=b(2-1/n)+c.

In order to realize a practically usable small and thin optical pick-uphead, a=2 mm, n=2.2 and a thickness t of the multi-plane parallel plate12 has to be 2 mm. Then, the distance a from the light emanating pointof the multi-image plane parallel plate 12 to the photodetector 18becomes about 1.5 mm. Therefore, it is practically difficult to mountthe optical elements onto a housing which is machined usually while theabove mentioned errors (1), (3) and (4) are restricted within givenranges. Moreover, the adjustment in the three axes within such a smallspace might cause an increase in the number of adjusting steps. When athickness t of the multi-image plane parallel plate 12 has an error ofΔt, the conjugate position b(2-1/n)+c deviates by about b·Δt/t.Therefore, the above condition (2) can be substantially satisfied if Δtis limited smaller than ±10 μm. A thickness t of the multi-image planeparallel plate 12 may be adjusted into a desired value by sliding thefirst and second triangular prisms relative to each other along theircontact surfaces upon joining the prisms.

FIG. 12 is a schematic view showing a second embodiment of the opticalpick-up head according to the invention. In the present embodiment,portions similar to those of the first embodiment are denoted by thesame reference numerals used in FIG. 3. In this embodiment, in order tosatisfy the above mentioned conditions (1) positioning precision of thesemiconductor laser, (3) positioning precision of the multi-image planeparallel plate and (4) positioning precision of the signal detectingphotodetector, a substrate 31 of a housing has positioning guides 32 ina form of recess or projection. Such a substrate 31 is formed by aphotolithography method, in which as a preparatory process, aphoto-mechanical process by a light reduction method is carried out andin a post process, material removal is carried out by etching andmaterial addition is performed by electroplating, The semiconductorlaser 11, multi-image plane parallel plate 12, signal detectingphotodetector 18, monitoring photodetector 14 and 45° rotator 15 aremounted on the substrate 31 while they are placed in position by usingthe positioning guides 32.

The semiconductor laser 11 is secured to a heat radiating stem 33 suchthat a light emitting point becomes coincided with an end face, and thestem 33 is mounted on the substrate 31 such that positioning of thesemiconductor laser 11 in the direction of the optical axis and onedirection of two orthogonal directions on a plane perpendicular to theoptical axis are defined by the positioning guides 32, so that uponmounting the stem 33 on the substrate 31, it is necessary to perform theadjustment only in the other direction of the two orthogonal directions.The signal detecting photodetector 18, monitoring photodetector 14 and45° rotator 15 are positioned by the positioning guides 32 only indirections of respective optical axes, so that the adjustment has to becarried out in two orthogonal directions on respective planesperpendicular to the optical axes. The incident surface of the firsttriangular prism 19 of the multi-image plane parallel plate 12 on whichthe polarizing film 13 is applied as well as the exit surface of thesecond triangular prism 20 from which the light beams emanate arepositioned by the positioning guides 32 and the two dimensionaladjustment on these planes of the first and second prisms 19 and 20 iscarried out. The function of the optical elements is entirely same anthat of the first embodiment, so that it is not explained here.

Since the positioning guides 32 of the substrate 31 are formed by thephotolithography method, and thus the machining precision can beimproved as compared with usually machining, and thus the opticalelements can be mounted on the substrate 31 easily and precisely. In thepresent embodiment, all the optical elements including the objectivelens 16 as illustrated in a chain line can be mounted on the singlesquare substrate 31 having a side of 7 mm.

In the present embodiment, optical elements are inserted along thepositioning guides, and therefore particularly semiconductor laser 11,multi-image plane parallel plate 12 and signal detecting photodetector18 are subjected to so-called Abbe's error of θ·h as the above mentionedother error (5), wherein h is a distance from a substrate bottom to anoptical axes of an element and θ is an inclination angle with respect tothe optical axis. When this error has to be kept not larger than ±10 μmunder a condition of h=1 mm, it is sufficient to restrict θ not largerthan ±5°. This condition can be relatively easily satisfied.

Upon adjusting a position of the signal detecting photodetector 18 inthe two orthogonal directions on the plane perpendicular to the opticalaxis, i.e. x' and y' directions in FIG. 12, it is preferable to utilizean optical device which can return a parallel light beam emanating fromthe optical unit to the optical unit at it is, while a collimator lens34 is secured to the optical unit. When the infinite optical system isconsidered, such an optical device can be realized by corner cube prismor cat's eye lens including a lens and a mirror arranged at a focalpoint of the lens. In this case, when the collimator lens 34 is securedto the optical unit as shown by a chain line in FIG. 12, the postprocess can be made easy.

In the present embodiment, the optical elements are mounted on thesubstrate 31 of the housing by utilizing the positioning guides 32formed by the photolithography, and therefore machining precision forthe substrate 31 becomes most important. The substrate 31 may bemanufactured by an isotropic machining including under or side etchingand an anisotropic machining without side etching.

In case of the isotropic machining, in order to attain a requiredprecision, it is preferable to design a photomechanical size byconsidering an etching margin due to the under cut and an electroplatingmargin. At the same time, it is preferable to use a standard pattern formonitoring a finished size of a work piece during the machining process.

In the anisotropic process, it is preferable to utilize a dependency ofan etching speed of a substrate material such as a single crystalsilicon for a solution of an enchant such as KOH (potassium hydroxide)upon an orientation of the crystal. In this case, an etching rate of acrystal plane (111) of a silicon single crystal is extremely smallerthan those of other planes, and a maximum etching rate is obtained for acrystal plane (110). A ratio of these etching rates amounts to 1:180. Byutilizing ouch a property, it is possible to form a deep recess 43 in asurface of a silicon wafer 41 as shown in FIG. 13, by performing anisotropic etching by providing a mask having an aperture extending in<112> or <112> direction on a (110) surface of the silicon wafer 41. Inthis manner, it is possible to form a deep recess 43 having {111}upright side walls 42.

In the manner explained above, by etching the (110) silicon waver 41such that {111} surfaces become the upright side wall 42 and {111}surfaces become bottoms, it is possible to obtain a recess having a highaspect ratio and a depth of 500 μm while an error in a width can berestricted not larger than 3 μm. The anisotropic etching of siliconsingle crystal has been explained in detail in Japanese Publication,Sato, "Anisotropic Etching Technique for Single Crystal Silicon",Precision Machinery Engineering Society, Vol. 53, No. 6, 1987, pp.849-852.

In the optical unit encircled by a chain line in FIG. 12, a micron orderprecision is required. In general, the fine adjustments in threedirections in the x'z plane, i.e. the x' and z directions and adirection inclined by 45° with respect to these axes are required. Thiscan be satisfied by using the substrate formed by the anisotropicetching.

FIGS. 14A to 14C are schematic views showing a third embodiment of theoptical pick-up head according to the invention. In the presentembodiment, a substrate unit 51 is formed by joining lower substrate 52and upper substrate 53. The lower substrate 52 is formed by a siliconsingle crystal wafer having a crystal plane denoted in FIG. 14A andhaving a thickness of about 1 mm. In this lower substrate 52 there areformed recesses having a depth of about 500 μm for accommodating andpositioning optical elements. In the present embodiment, the opticalsystem is same as that of the second embodiment shown in FIG. 12,Therefore, the lower substrate 52 has formed therein a recess 54 for thesemiconductor laser 11, a recess 55 for the multi-image plane parallelplate 12, a recess 56 for the signal detecting photodetector 18 and arecess 57 for the monitoring photodetector 14. Therefore, the recesses54, 56 and 57 have required precision in the <111> direction. It shouldbe noted that the recess 55 has a size slightly larger than themulti-image plane parallel plate 12.

The upper substrate 53 shown in FIG. 14B in formed by a single crystalsilicon wafer having a thickness of about 0.1-0.3 mm. In the uppersubstrate 53 there are formed, by the anisotropic etching, a cut-outportion and through holes for positioning and mounting the abovementioned optical elements. That is, a out-out portion 58 for thesemiconductor laser 11, a hole 59 for the multi-image plane parallelplate 12, a hole 60 for the signal detecting photodetector 18 and a hole61 for the monitoring photodetector 61. Therefore, the hole 59 forpositioning and mounting the multi-image plane parallel plate 12 has arequired precision in the <111> direction. It should be noted that thecut-out portion 58 and holes 60 and 61 are formed to be slightly largerthan the corresponding optical elements 11, 18 and 14.

The lower and upper substrates 52 and 53 are relatively positioned byutilizing previously formed positioning marks, and then are jointedtogether by direct contact or anodic junction. After that, an assemblyis cut to form the substrate unit 51 shown in FIG. 14C. In the presentembodiment, it is possible to perform the positioning in two directions.If one more substrate is added, it is possible to perform thepositioning in three directions. In the present embodiment, the outputpower of the semiconductor laser 11 is monitored by receiving the laserbeam reflected by the polarizing film 13.

In a modification of the third embodiment, use is made of a substratehaving formed therein positioning guides which can perform thepositioning in three directions with micron order. Such a substrate canbe manufactured by a lithography technique called LIGA process havingexcellent linearity, resolution and transmission. In this LIGA process,use is made of an X-ray called SOR radiation emitted by a synchrotronand a deep recess having a high aspect ratio can be formed preciselywith micron order even if a resist has a thickness of about 1 mm.

It should be noted that when (110) silicon single crystal wafer is usedas the substrate of the integrated type optical unit of the opticalpick-up head and the anisotropic etching is carried out, (111) surfacesappear in two directions, so that upright side walls having these (111)surfaces may be utilized for positioning. However, in this case, theside walls are not perpendicular to each other. Furthermore, by usingsuch a substrate it is possible to form a substrate having requiredprecision in three directions.

Moreover, the integrated type optical unit according to the inventionmay be applied to an optical record medium other than themagneto-optical record medium. In the so far explained embodiments, abeam shaping faculty may be adopted in order to change an ellipticalcross section of the laser beam emitted by the semiconductor laser intoa circular cross section.

In the above mentioned embodiments of the optical pick-up head accordingto the invention, the multi-image plane parallel plate with thepolarizing film is provided with the polarizing beam splitting functionfor separating the return beam from the incident beam, the polarizingbeam splitting function for detecting the MO signal from the return beamby the differential method and the astigmatism generating function forintroducing the astigmatism for detecting the FES, and further theastigmatism is generated in a direction which is inclined by 45° withrespect to the information track on the optical record medium.Therefore, the optical unit can be small in size, light in weight andcheap in cost, and furthermore leakage of the PP signal into the FES canbe effectively prevented so that the focus servo can be performedaccurately and stably.

Further, in the above mentioned embodiments of the integrated typeoptical unit according to the invention, the semiconductor laser, signaldetecting photodetector and beam splitting element are positioned andmounted on the substrate having the positioning guides formed bylithography, and thus the assembling can be performed easily andprecisely, while the optical unit can endeavor sever conditions.

FIG. 15 is a schematic view showing a basic construction of the opticalpick-up head according to the invention. In the present embodiment,portions similar to those of the previous embodiments are denoted by thesame reference numerals used in the previous embodiments. An integratedtype optical unit 71 comprises semiconductor laser 11, signal detectingphotodetector 18 and a beam splitting member 72 for separating a returnlight beam L _(R) from an incident light beam L_(I). A laser beamemitted by the semiconductor laser 11 is reflected by the beam splittingmember 72 and is focused on an optical record medium 17 by means of anobjective lens 16 as a fine spot.

The return beam reflected by the optical record medium 17 is madeincident again upon the beam splitting member 72 by means of theobjective lens 16 and is transmitted through the beam splitting member.The return beam emanating from the beam splitting member 72 is madeincident upon the signal detecting photodetector 18, and FES, TES and MOsignal can be derived by processing outputs of the photodetector 18.

The beam splitting member 72 may be formed by semi-transparent plate orprism utilizing reflection and transmission, grating in which theincident beam is obtained as a zero order beam and the return beam isdivided into higher order beams, polarizing beam splitter constructingan optical isolator together with a 1/4 wavelength plate.

Now it is assumed that a distance between the semiconductor laser 11 andthe beam splitting member 72 is a and a distance between the beamsplitting member and the signal detecting photodetector 18 is b. Whena=b, the semiconductor laser 11 and the photodetector 18 becomeoptically conjugate. Therefore, by mounting and positioning theseelements as the integrated type optical unit 71, interference isintroduced into the common optical path, an optical property is notdisturbed.

It should be noted that the positions of the semiconductor laser 11 andphotodetector 18 may be exchanged mutually. In this case, the light beamemitted by the semiconductor laser is transmitted through the beamsplitting member 72 and the return beam is reflected by the beamsplitting member. Moreover, if a reflecting member is arranged behindthe beam splitting member in the optical path of the return beam, thesemiconductor laser and photodetector may be arranged on the same sideof the beam splitting member.

FIG. 16 is a schematic view depicting a fourth embodiment of the opticalpick-up head including the integrated type optical unit illustrated inFIG. 15. The optical pick-up head according to the present embodiment isused for the magneto-optical record medium and is constructed inaccordance with the infinite method. A diverging linearly polarizedlaser beam emitted by a semiconductor laser 11 is made incident upon amulti-image plane parallel plate 12 having a polarizing film applied onan incident surface. A light flux transmitted through the polarizingfilm 13 and multi-image plane parallel plate 12 is received by amonitoring photodetector 14 and an output power of the semiconductorlaser 11 is controlled in accordance with an output of the photodetector14, A light flux reflected by the polarizing film 13 is converted into aparallel beam by means of a collimator lens 73 and then the parallelbeam is focused by an objective lens 16 on an information track 17a of amagneto-optical record medium 17 an a very small spot.

A return beam reflected by the magneto-optical record medium 17 is madeincident upon the polarizing film 13 by means of the objective lens 16and collimator lens 73 and is transmitted through the polarizing film13. In this manner, the return beam is separated from the incident beamand is made incident upon the plane parallel plate 12. The return beamimpinging upon the plane parallel plate 12 is transmitted through andrefracted by the plane parallel plate, so that astigmatism is introducedinto the return beam. At the same time, the return bean is divided intoa plurality of beams by the polarizing beam splitting function of theplane parallel plate 12, and these light beams are received by a signaldetecting photodetector 18. By suitably processing outputs of thephotodetector 18, it is possible to derive MO signal, FES and TES.

The plane parallel plate 12 is formed by two triangular prisms 19 and 20made of birefringent material. In the present embodiment, the prisms 19and 20 are made of lithium niobate and optic axes of these prisms arearranged in the same manner as that of the first embodiment illustratedin FIGS. 3 to 6. Therefore, from the plane parallel plate 12 there areemanated three light beams OE, EO and OO+EE. These three light beams arereceived by three light receiving units 21, 22 and 23 of the signaldetecting photodetector 18 as shown in FIG. 17. The signal detectingphotodetector 18 receiving the return beam emanating from the planeparallel plate 12 is arranged at a beat image point of the astigmatismintroduced by the plane parallel plate, i.e. a middle point between afocal point in the x' direction and a focal point in the y' direction.

Also in the present embodiment, the MO signal can be obtained byderiving a difference between outputs of the light receiving units 21and 22, the FES can be attained by the differential method, and the TEScan be obtained by the PP method. A ratio of intensities of the lightbeams impinging upon these light receiving units 21, 22 and 23 may beset at will by suitably selecting an angle formed by the optic axes ofthe first and second triangular prisms 19 and 20. Further, when saidangle is set to 90° to form the plane parallel plate 12 as a Wollaston'sprism, an intensity of the light beam (OO+EE) becomes zero. Then, thesignal detecting photodetector 18 may include two light receiving units21 and 22 as illustrated in FIG. 9.

FIGS. 18A and 18B are schematic side and plan views of a fifthembodiment of the optical pick-up head according to the inventionincluding the integrated type optical unit. In the present embodiment,in a mounting substrate 81 made of silicon wafers and having a (110)upper most surface, there are formed upright recesses and upright wallshaving (111) side walls, and semiconductor laser 11, multi-image planeparallel plate 12, monitoring photodetector 14 and signal detectingphotodetector 18 are mounted on the substrate 81 by utilizing the sidewalls as positioning guides, while these elements are adjusted at leastin optical axes thereof.

The upright recesses and upright walls having the {111} side walls canbe formed in the silicon wafer precisely by utilizing the anisotropicetching which has been widely used in the precise machining field. Asexplained above, by performing the isotropic etching by providing a maskhaving an aperture extending in <112> or <112> directions on an upper(110) surface of the silicon wafer, it is possible to form deep recessesup to 500 μm with an error in a direction of width smaller than 3 μm dueto the fact that the extremely large ratio of the etching rate forcrystal plane (110) to the etching rate for crystal plane (111). Theratio in these etching rates may amount to 180:1. For instance, it ispossible to form a recess having 1.2 mm with an error in a direction ofa width can be kept smaller than 7 μm.

The mounting substrate 81 is formed by (110) silicon wafers 82 and 83which are jointed together by means of an etching stopper layer 84. Whenthe upper surface of the silicon wafer is set to (110), there are formedfour upright side walls of (111) and angles between these side wallssurfaces become 109.5° and 70.5° as shown in FIG. 19A. Therefore, it ispossible to form recesses 85, 86 and 87 having {111} upright side wallsas shown in FIG. 18B by the anisotropic etching. A thickness of thefirst and second silicon wafers 82 and 83 is preferably set to 0.3-0.5mm.

In case of forming the {111} walls in the (110) silicon wafer by theanisotropical etching, the following two points should be taken intoaccount.

First, there are formed two (111) surfaces in a bottom of a recess whichare not parallel with the upper surface of the silicon wafer in additionto the four upright (111) side walls. FIG. 19B is a cross sectional viewof the recess formed in the silicon wafer by the anisotropic etching cutalong the z axis and viewed from an arrow a in FIG. 19A. As shown inFIG. 19B, said two (111) surfaces are inclined by 35.3° with respect tothe upper surface of the wafer, There inclined surfaces start fromopposite corners having an angle of 70.5°. An area of the inclinedsurface is gradually increased in accordance with a progress of theetching, and finally the two inclined (111) surfaces are joined togetherso that the bottom of the recess is fully formed by the inclinedsurfaces, This will be further explained with reference of FIGS. 20A,20B and 21A, 21B. FIG. 20A is a plan view and FIG. 20B is a crosssectional view cut along a line A--A in FIG. 20A, and FIG. 21A is a planview and FIG. 21B is a cross sectional view cut along a line A--A inFIG. 21A. FIGS. 20A and 20B illustrate a configuration of a recessduring an etching process, in which (111) inclined surfaces are formedin a part of a bottom of the recess, and FIGS. 21A and 21B depict thesame at an end of the etching process, in which the whole bottom surfaceis formed by the inclined surfaces. The anisotropic etching isautomatically stopped in the condition shown in FIGS. 21A and 21B andall walls defining the recess are formed by (111) surfaces. Therefore, asize of an etching mask corresponding to the corners of 70.5° has to bedesigned by considering a necessary depth of the recess and a requiredarea of a flat bottom portion. When a depth of the recess is representedby d, a flat bottom portion can be formed from a point which isseparated from the 70.5° corner by a distance 1=d/tan35.5°.

Second, due to the etching there appear higher order surfaces at aconvex corner, so that the corner is liable to be rounded and a requiredprecision could not be obtained. In order to mitigate such a drawback,it is preferable to correct a configuration of the mask. This has beenexplained in detail in B. Puers and W. Sansen, "Compensation Structuresfor Convex Corner Micro machining in Silicon", Sensors and Actuators,A21-A23, 1990, pp. 1036-1041.

Now the structure of the optical unit illustrated in FIGS. 18A and 18Bwill be further explained in detail. The semiconductor laser 11 issecured to a stem 88 made of good heat conducting material such as metaland the stem is mounted in the recess 85. When the semiconductor laser11 is secured to the stem 88, the semiconductor laser is positioned withrespect to the stem. In the recess 86, the multi-image plane parallelplate 12 as well as the monitoring photodetector 14 are positioned andmounted. The signal detecting photodetector 18 is positioned and mountedin the recess 87.

In the present embodiment, thicknesses of the optical elements haverequired precision, and they are mounted on the substrate 81 while thepositioning in the z axis is carried out. Therefore, for thesemiconductor laser 11 and signal detecting photodetector 18, thepositioning in the x' and y' directions Is required. However, if theoptical elements have micron order precision also in the x' and y'directions, it is no more necessary to perform the positioning in thesex' and y' directions. Further if a required precision is attained in oneof the x' and y' directions, it is necessary to carry out positioningonly in the other direction. In this manner, the process of positioningcan be simplified.

Also in the present embodiment, the positioning of the optical elementsin the x' and y' directions can be performed by using an optical systemwhich can return a parallel light beam toward a light source such ascorner cube prism and cat's eye lens system,

In the present embodiment, all the optical elements shown in FIG. 11Bcan be mounted on the square substrate having a side of 7 mm. It shouldbe noted that the present embodiment may be applied not only to theoptical head for the magneto-optical record medium but also to any typeof optical head including at least semiconductor lager photodetector andbeam splitting element.

FIG. 22 is a schematic view showing an integrated type optical unit of asixth embodiment of the optical pick-up head according to the invention.In the present embodiment, a silicon substrate 91 comprised a recess 92for mounting the semiconductor laser 11, a recess 93 for mounting themulti-image plane parallel plate 12 formed by the triangular prisms 19and 20 made of birefringent material and a recess 94 for mounting thesignal detecting photodetector 18. In FIG. 22, the monitoringphotodetector and a recess therefor are not shown for the sake ofsimplicity, The mounting substrate 91 is formed by anisotropicallyetching (110) silicon wafer like as the fifth embodiment. In the presentembodiment, the recesses 92 and 93 for mounting the stem 88 to which thesemiconductor laser 11 is secured and the multi-image plane parallelplate 12 have sawtooth-shaped side walls.

In the present embodiment, there are formed spaces between the stem 88and multi-image plane parallel plate 12 and the upright side walls ofthe recesses 92 and 93, and an excessive amount of a adhesive agent canflow into these spaces. It should be noted that a recess havingsawtooth-shaped upright side walls can be formed in various shapes asshown in FIGS. 23A, 23B and 23C. In FIG. 23A, side walls are formed tohave convex corners of 109.5°, in FIG. 23B side walls are formed to haveconvex corners of 70.5°, and in FIG. 23C side walls are formed to haveconvex corners of 70.5° and 109.5°.

FIGS. 24A, 24B and 24C illustrate the integrated optical unit of aseventh embodiment of the optical pick-up head according to theinvention. In the present embodiment, a mounting substrate 101 is formedby anisotropically etching a (100) silicon wafer and recesses 102-105having inclined side walls are formed with a precision of micron order.In the specification, there recesses 102-105 are called pyramidrecesses. The inclined side walls of the pyramid recesses 102-105 areformed by (111) surfaces which are inclined by about 54.7° with respectto an upper surface of the mounting substrate 101.

In bottoms of the pyramid recesses 102-105 there are formed throughholes 106-109 respectively and these through holes are communicated withan air suction device 110 as shown in FIG. 24C so that optical elementscan be positioned in respective pyramid recesses by the air suctionforce. That is, the stem 88 having the semiconductor laser 11 securedthereto is positioned and mounted in the pyramid recess 102, themulti-image plane parallel plate 12 is positioned and mounted in thepyramid recess 103, the signal detecting photodetector 18 is positionedand mounted in the pyramid recess 105 and the monitoring photodetector14 is positioned and mounted in the pyramid recess 105. In this case,the inclined side walls of respective pyramid recesses 102-105 serve ancollets for receiving respective optical elements, and thus veryaccurate positioning matched to precision of abutment surfaces can berealized. In this case, the etching proceeds in such a manner that asize of a bottom surface is reduced while a pyramid shape having a sizecorresponding to the mask aperture, and therefore a required precisionfor the abutment surfaces of the pyramid recesses can be obtainedalthough an etching time is prolonged to some extent.

As can be seen from FIGS. 24A and 24B, the stem 88 and photodetectors14, 18 can be placed in position by the air suction force into thepyramid recesses 102, 104 and 105, respectively, because these recesseshave configurations corresponding to these optical elements. However,the multi-image plane parallel plate 12 is inclined by 45° with respectto the sides of the pyramid recess 103, and thus this plate could not bedirectly positioned and mounted in the pyramid recess. In the presentembodiment, on a rear surface of the multi-image plane parallel plate 12is secured a square stud 111 as shown in FIG. 25A and this stud 111 ispositioned and mounted into the pyramid recess 102 an depicted in FIG.25B. The stud 111 may be formed by etching a (100) silicon wafer.

FIGS. 26A, 26B and 26C illustrate another method of positioning andmounting the multi-image plane parallel plate 12 into the pyramid recess102. In this method, a mounting member 112 in formed by anisotropicallyetching a (100) silicon wafer to have a pyramid recess 113 and a throughhole 114 is formed in a bottom of the pyramid recess 114 as shown inFIG. 26A. Then, the multi-image plane parallel plate 12 is positionedand mounted onto the pyramid recess 113 by utilizing the air auctionforce. Then, the mounting member 112 having the plate 12 mounted thereonis positioned and mounted onto the pyramid recess 102 formed in themounting substrate 101 by utilizing the air suction force an shown inFIG. 26C.

In the present embodiment, the optical elements are positioned andmounted in the mounting substrate 101 having pyramid recesses includingthe inclined side walls serving as collets, so that an error in mountingcan be less than about ±5 μm.

Upon mounting the optical elements on the mounting substrate 101 byutilizing the air suction force like as the collet, a substrate similarto the (100) silicon wafer shown in FIG. 24A may be used a collet jigfor positioning and mounting the optical elements onto the mountingsubstrate 101. FIG. 27A shows such a collet jig 121. In which pyramidrecesses 122-125 are formed by the anisotropic etching and through holes126-129 are formed in respective recesses. The collet jig 121 has anentirely same configuration as that of the mounting substrate 101.

As illustrated in FIG. 27B, the collet jig 121 is secured to an arm 131which can be moved very accurately. Given optical elements 132 areplaced on a platform 133. At first, the arm 131 is moved toward theplatform 133 and the optical elements 132 on the platform aretransferred to the collet jig 121 by the air suction force. Then the arm131 having the collet jig 121 secured thereto is moved away from theplatform 133 and is then moved toward a platform 134 on which themounting substrate 101 is placed as shown in FIG. 27C. Then, the opticalelements 132 supporting by the collet jig 121 are transferred onto themounting substrate 101 and are secured thereto by an adhesive agentsupplied from a dispenser nozzle 135. The arm 131 is constructed to movebetween the platform 133 having the collet jig 121 and the platform 134supporting the mounting substrate 101 in a precise manner. Platforms 134supporting mounting substrates 101 may be successively indexed into anoptical element mounting position.

In the manner explained above, the optical elements 132 can bepositioned and mounted on the mounting substrate 101 with a micron orderprecision. In this method, the mounting substrate 101 may be replaced bya simple mounting substrate having a flat upper surface. Moreover, allthe optical elements 132 may be transferred to the collet jig 121simultaneously and then after aligning heights of the optical elementson a same plane, all the optical elements may be transferred to themounting substrate 101 simultaneously. Alternatively, the opticalelements may be transferred one by one.

FIGS. 28A to 28E show a mounting substrate unit of the integrated typeoptical unit of an eighth embodiment of the optical pick-up headaccording to the invention. In this embodiment, the mounting substrateunit comprises a base substrate 141 depicted in FIG. 28A, a spacersubstrate 142 shown in FIG. 28B and a positioning substrate 143illustrated in FIG. 28C. The base substrate 141 is formed by a siliconwafer having a thickness of about 0.5 mm. The spacer substrate 142 isformed by anisotropically etching a (100) silicon wafer having athickness of about 0.3-0.5 mm and has formed therein an opening 144defined by inclined side walls 145. The positioning substrate 143 shownin FIG. 28C is formed by anisotropically etching a (110) silicon waferhaving a thickness of about 0.1-0.2 mm and has an opening 146 defined byupright side walls and inclined surfaces 147. After forming the spacersubstrate 142 and positioning substrate 143 are formed by the etching,the are placed on the base substrate 141 in position and these threesubstrates are joined with each other by adhesive agent as depicted inFIG. 28D. FIG. 28E is a cross sectional view of the thus formed mountingsubstrate unit 147 cut along a line A--A in FIG. 28D.

In the present embodiment, it is possible to form a deep recess comparedwith a recess formed in a (110) silicon wafer by the anisotropicetching, so that the positioning precision of the optical elements canbe further improved. It should be noted that the positioning substrate143 may be formed from a (100) silicon wafer. In this case, an openingformed in a positioning substrate 148 formed by a (100) silicon wafer isdefined inclined side walls 149 as shown in FIG. 28F. These inclinedside walls 149 serve as guides for the insertion of an optical element,so that the positioning and mounting step can be carried out easily.

FIGS. 29A to 29C show a mounting substrate unit of the integrated typeoptical unit of a ninth embodiment of the optical pick-up head accordingto the invention. In the present embodiment, on a base substrate 151 issecured a spacer substrate 152 and a polyimide film 153 having athickness of about 100 μm is applied on a surface of the spacersubstrate 152. At first, a mask having a given opening is provided inthe polyimide film 153 and then an opening 154 is formed in thepolyimide film 152 to expose the underlying spacer substrate 152 asdepicted in FIG. 29A by a&reactive ion etching (RIE). Then, the spacersubstrate 152 is subjected to an isotropic etching via the opening 154to form a recess 155 extending to a surface of the base substrate 151.The isotropic etching may be performed by using an etchant HF+NHO₃. Inthis manner, a mounting substrate unit 156 shown in FIG. 29C can beobtained. FIG. 29C is a cross sectional view cut along a line A--A inFIG. 29B. The base substrate 151 may be made of a material which canstop the isotropic etching or a thin polyimide or nitride film servingas a stopper for the isotropic etching may be applied on a substrate.

Like as the embodiment shown in FIGS. 28A to 28F, in the presentembodiment, it is possible to form a deep recess having small inclined(111) side walls as compared with the mounting substrate which is formedby anisotropically etching a single (110) silicon wafer, and thereforethe optical elements pan be positioned very precisely. Moreover, in thepolyimide film 153, it in possible to form the opening 154 having alarge depth up to 100 μm by the reactive ion etching with a side orunder etch of several micron meters. Further, the spacer substrate 152is etched isotropically, it is possible to form a positioning patternextending in any direction, Instead of "polyimide+RIE", it in alsopossible to adopt "thick resist+UV expose" or "photosensitivepolyimide+UV expose".

FIG. 30 is a schematic view showing the integrated type optical unit ofa tenth embodiment of the optical pick-up head according to theinvention. In the previous embodiments of the integrated type opticalunit, the optical elements are positioned with reference to the sidewalls of the recesses and cut out portions, but in the presentembodiment, the optical elements are positioned with reference toupright walls protruding from a surface of a mounting substrate. In FIG.30, positioning projections are denoted by hatching, A mountingsubstrate 201 is formed by anisotropically etching a (110) silicon waferto remove silicon material other than the positioning projections by adepth of 1.2 mm. In FIG. 30, surface except for upper and lower surfacesand a left side wall are formed by (111) upright walls obtained by theetching. A right side wall is formed by a (111) upright wall having aheight of 1.2 mm and a remaining wall portions having a thickness of 0.5mm is formed by dicer cut. A left upright wall of a left lowerprojection 202 is coated with a film for joining the semiconductor laser11 and the semiconductor laser 11 is positioned with a junction down inorder to dissipate a heat from the semiconductor laser 11 and is mountedon the upright wall of the projection 202. The multi-image planeparallel plate 12 is arranged in position by means of 109.5° corners ofprojections 203 and 204 such that the plate could not be rotated and issecured to these corners by an adhesive agent. It should be noted that arotation of the multi-image plane parallel plate 12 does not affect theconjugate distance between the semiconductor laser 11 and the signaldetecting photodetector 18 so much, and therefore a rather large erroris allowed for a size of the corners of the projections 203 and 204.

Projections 205 and 206 are formed such that their right hand uprightwalls aligned in a same plane and the signal detecting photodetector 18is mounted on theme right hand upright walls of the projections 205 and206 such that a position of the photodetector 18 can be adjusted in x'and y' directions. Upper upright walls of the projections 204 and 205are aligned in a same plane, because these upright walls are formed bythe dice cut. The monitoring photodetector 14 is mounted on theme upperupright walls of the projections 204 and 205 such that a position of thephotodetector can be adjusted in y' and z directions. To thephotodetectors 14 and 18 are secured wiring submounts 207 and 208,respectively.

The optical elements 11, 12, 14 and 18 have a height of about 1 mm andthe optical axes of these elements are set substantially at a middlebetween the upper and lower surfaces of the mounting substrate 201. Itshould be noted that positioning projections 202-206 have to be formedsuch that they do not interrupt the optical path. In the presentembodiment, although the projections 202-206 having a relatively largeheight are formed by the etching, there is not formed an inclinedsurface in the surface of the substrate 201, so that a corner of 70.5°is not used in the etched recess. Moreover, even if inclined (111)surfaces are formed due to adjacent patterns to be formed in the siliconwafer, bottom portions in areas at which the optical elements aremounted are formed to be flat.

In the present embodiment, the semiconductor laser 11 and signaldetecting photodetector 18 are secured to the (111) upright walls havingthe same orientation and the multi-image plane parallel plate 12 issecured to the convex corners of the projections 203 and 204 in such amanner that the plate 12 is not rotated, and therefore the opticalconjugating relationship of the semiconductor laser 11, multi-imageplane parallel plate 12 and signal detecting photodetector 18 can beattained easily and these optical elements can be arranged in positionin the direction of the optical axes with an error of micron order.

In the present embodiment, the signal detecting photodetector 18 isadjusted in the x' and y' directions, but if the photodetector can bemanufactured to have a precision of micron order in the x' and y'directions, the above adjustment may be dispensed with. Moreover, if arequired precision can be attained in the y' direction, it is necessaryto perform only in the x' direction.

The adjustment in the x' and y' of optical elements can be carried outby using the corner cube prism or cat's eye lens for the infiniteoptical system having a collimator lens which is coupled with theoptical unit.

In the manner explained above, in the present embodiment, all theoptical elements shown in FIG. 30 can be mounted on the mountingsubstrate 201 having a size of 3.5 mm×7 mm×1.7 mm. The optical unitshown in FIG. 30 may be used not only for the optical informationreading and/or writing apparatus using the magneto-optical recordmedium, but also for an apparatus for reading and/or writing informationfrom and/or on any type of optical record medium.

FIG. 31 is a perspective view depicting a part of the integrated typeoptical unit of an eleventh embodiment of the optical pick-up headaccording to the invention, In the present embodiment, a mountingsubstrate unit 220 is formed by joining a (110) silicon wafer 222 on a(100) silicon wafer 221 having a thickness of about 0.5 mm via anetching stopper layer 223 made of, for instance SiO₂. The joining may becarried out by direct joining or anode joining. The (119) silicon wafer222 is subjected to the anisotropic etching to form projections 224-227having upright walls and optical elements are mounted on the (110)silicon substrate 222 like as the embodiment shown in FIG. 30. In FIG.31 only the multi-image plane parallel plate 12 and signal detectingphotodetector 18 are shown. By providing the etching stopper layer 223,a precision of etching depth and A flatness of the etched bottom can beattained easily, and thus the etching process can be conducted easily.

In the present embodiment, in order to facilitate the adjustment ofoptical elements in x' and/or y' directions and to prevent adisplacement of the optical elements during a cure period of an adhesiveagent, air sucking holes are formed in the projections. As shown in FIG.31, holes 228 and 229 are formed in the projections 226 and 227,respectively for mounting the signal detecting photodetector 18. FIG. 32is a cross sectional view cut along a line A--A in FIG. 30 and shows thehole 229 formed in the projection 227. As shown in FIG. 32, the hole 229is communicated with a hole 230 formed in the (100) silicon substrate221.

Now a method of forming the holes 228, 229 will be explained. At first,the holes 228 and 219 are formed the (110) silicon substrate 222 byetching from a rear surface thereof. In this case, a length and a widthof a mask for the etching are determined such that the etching isautomatically stopped at a depth of about 0.8-1 mm due to inclined (111)surfaces. The etching stopper layer 223 is provided on the surface ofthe (100) silicon wafer 221 and the hole 230 is formed by etching in the(100) silicon wafer via an opening 231 formed in the etching stopperlayer 223. Then, the (110) silicon wafer 222 is joined on the (100)silicon wafer 221 via the etching stopper layer 223 and the (110)silicon wafer is subjected to the anisotropic etching to form theprojections for mounting the optical elements. In this case, thepreviously formed air suction holes are defined by (111) surfaces, sothat a shape of these holes is not changed during anisotropic etchingfor forming the projections.

FIGS. 33A, 33B and FIGS. 34A, 34B illustrate shapes of a recess formedin a (100) silicon wafer by the anisotropic etching. In case ofanisotropically etching the (100) silicon wafer, there is formed apyramid recess and side walls are inclined by 54.7° with respect to anupper surface. FIGS. 33A illustrates a condition during the etching andFIG. 33B is a cross section cut along a line A--A in FIG. 33A. In thisstate, there is still remained a (100) bottom surface other than thefour inclined (111) surfaces. The etching is automatically stopped in acondition shown in FIG. 34A. The recess is finally defined by the four(111) surfaces. Therefore, when a short side of the rectangle is denotedby 21, a depth d of the recess amounts to 1×tan 54.7°. Therefore, athickness of the silicon wafer is smaller than the depth d of therecess, there can be formed the through holes in the (100) siliconwafer.

The (110) silicon wafer and (100) silicon wafer processed in the mannerexplained above are then joined together and the air suction holes 228and 229 communicated with the holes 230 formed in the (100) siliconwafer 221 are obtained. By sucking an air through these holes, thephotodetector 18 can be sucked to the right upright side walls of theprojections 226 and 227 and thus can be easily adjusted in the x' and y'directions. Further, during a cure period of an adhesive agent, thephotodetector 18 can be kept in position. It should be noted that suchair suction holes may be formed for other optical elements such as thesemiconductor laser 11 and monitoring photodetector 18.

FIG. 35 is a schematic view showing the integrated type optical unit ofa modification of the tenth embodiment of the optical pick-up headaccording to the invention shown in FIG. 30. In this modifiedembodiment, the mounting substrate 201 further comprises a mounting andpositioning projection 209 and its 70.5° convex corner is used as aguide for positioning the semiconductor laser 11 in the optical axis.The remaining construction of this modification is identical with thetenth embodiment depicted in FIG. 30. As explained above, thesemiconductor laser 11 is mounted on the left hand upright side wall ofthe projection 202 with the junction down. The semiconductor laser 11has a thickness of about 100 μm and its light emitting plane isseparated by several micron meters from a surface which is secured tothe upright side wall of the projection 202. Therefore, the corner ofthe projection 209 can be brought into contact with a light emittingsurface of the semiconductor laser 11 without shielding the laser beamemitted by the semiconductor laser.

As shown in FIG. 35, the projection 209 is formed to be out of a regionextending from the optical axis of the laser beam by 25°-30°, so thatthe laser beam is prevented from being diffracted by the projection in anear field. Further, the positioning corner of 70.5° is formed with ahigh precision. In the present embodiment, the semiconductor laser 11 ispositioned by the projections 202 and 209 in the x' and z directions,and thus the relatively rough adjustment of the semiconductor laser inthe y' direction is required.

Advantages of the integrated type optical units according to theinvention may be summarized as follows:

(1) The optical elements can be mounted on the single mounting substrateor single mounting substrate unit precisely in a compact manner, so thatthe optical unit can be highly stabilized and can be made small in size,light in weight and cheap in cost.

(2) The semiconductor laser, beam splitting element and signal detectingphotodetector can be mounted such that distances between these elementsin the optical axes can be maintained with a precision of micron orderand thus the adjustment during the mounting can be extremely simplified.In case of adopting the infinite optical system, the adjustment can befurther simplified by using a simple optical system such as corner cubeprism and cat's eye lens. Since the adjustment in the x' and y'directions does not interfere with the adjustment in the z direction, itis possible to perform the adjustment by intermediate property values.

(3) The number of adjusting steps can be materially reduced, becauseonly the signal detecting photodetector or the signal detectingphotodetector and semiconductor laser require the adjustment,

(4) By using the optical elements having high precision, any adjustmentcan be dispensed with.

(5) The semiconductor laser, beam splitting element, signal detectingphotodetector and monitoring photodetector can be mounted on the singlemounting substrate having a very small size such as 3.5 mm×7 mm×1.7 mm.After mounting the optical elements, the mounting substrate isencapsulated and a package is filled with an inert gas. Then, a lifetime of the optical unit can be prolonged extremely.

(6) In the embodiments shown in FIGS. 30-35, the inclined (111) surfacedoes not appear in the etched bottom and the convex corner of 70.5° isutilized to position the semiconductor laser only in the optical axis,and thus a required precision can be easily attained.

(7) In the embodiments shown in FIGS. 30-35, the semiconductor laser andsignal detecting photodetector are positioned by the (111) surfacesoriented in the same direction and the multi-image plane parallel plateis mounted not to rotate, the distances between these elements measuredalong the optical axes can be kept with a precision of micron order.

FIGS. 36A and 36B show a twelfth embodiment of the optical pick-up headaccording to the invention. Also in the present embodiment, portionssimilar to those of the previous embodiments are denoted by the samereference numerals used in the previous embodiments. An integrated typeoptical unit 300 comprises a mounting substrate 301 on which a stem 88having a semiconductor laser 11 secured thereto, beam splitting elementsuch as a multi-image plane parallel plate 12, monitoring photodetector14 and signal detecting photodetector 18 are mounted in position. Theintegrated type optical unit 300 may be one of the previous embodiments.

In the present embodiment, a reference end surface 302 is formed in themounting substrate 301 such that the reference end surface isperpendicular to an optical axis of a light beam emanating from theoptical unit 300 toward a collimator lens 73. When the mountingsubstrate 301 is formed by anisotropically etching the (110) siliconwafer like in the previous embodiment, the reference end surface 302 canbe formed by the anisotropic etching. The reference end surface 302 maybe formed by a dicer cut using a precise pattern obtained byphotolithography.

In this manner, the optical elements of the integrated type optical unit300 are positioned and mounted on the mounting substrate 301 preciselyhaving the positioning recesses or projections. Therefore, a distance abetween a light emitting point of the semiconductor laser 11 to thereflecting surface of the beam splitting element 12 measured along the xdirection and a distance c between the light emitting point of thesemiconductor laser 11 to the reference end surface 302 can be preciselydetermined. In the present embodiment, the mounting substrate 301 has asize of 5 mm×4 mm.

FIGS. 37A and 37B are plan and side views showing an assembly of saidoptical unit 300 and a base member 310. In the base member 310 there areformed a unit mounting portion 311 for mounting the optical unit 300 anda collimator lens mounting portion 312 having a through hole 313. Theunit mounting portion 311 comprises an abutment surface 314 and theoptical unit 300 is positioned by urging the reference side surface 302against the abutment surface 314. In order to attain a positive surfacecontact between the reference end surface 302 and the abutment surface314, an escape portion 315 is formed in an upper surface of the basemember 310 in a vicinity of the abutment surface 314 as illustrated inFIG. 37B, In the collimator lens mounting portion 312, there is formed amounting surface 316 at an opening of the through hole 313, and thecollimator lens 73 is hermetically secured to this mounting surface 316.The base member 310 further comprises a flange portion 317, in whichholes 318 and 319 are formed for coupling the base member with a pick-upchassis or a main body of a disk driver.

In this construction, a distance between the semiconductor laser 11 andthe collimator lens 73, i.e. a distance a+b in FIG. 36A is determined bya focal length of the collimator lens. If this distance is determinedprecisely, the light beam emanating from the collimator lens 73 towardthe objective lens 16 and optical record medium 17 is not a parallelbeam, but is a converged or diverged light beam. Then aberrationsintroduced by the objective lens 16 become large and the informationreading and/or writing property is deteriorated. The distances a and cshown in FIG. 36A can be determined precisely by using the positioningmethod utilizing the semiconductor manufacturing process, but thedistance b between the reflecting surface of the beam splitting element12 and the mounting surface 316 for the collimator lens 73 measured inthe z direction in determined by the construction of the base member311. When the reference end surface 302 of the mounting substrate 301 inurged against the abutment surface 314 of the base member 311 as shownin FIGS. 37A and 37B, the distance b may be expressed by b=d-c, whereind in a distance between the abutment surface 314 and the collimator lensmounting surface 316. Therefore, if the distance d can be determinedprecisely, it is possible to delete the adjustment of the collimatorlens 73 in the direction of the optical axis with respect to the basemember 311.

In the present embodiment, the abutment surface 314 and collimator lensmounting surface 316 are set to be in parallel with each other, so thatsaid distance d can be easily determined precisely. When the abutmentsurface 314 an d collimator lens mounting surface 316 are formed to bein parallel with each other, they can be formed by a milling machinewith a precision smaller than 10 μm, while a posture of the base member311 with respect to the milling machine is not changed and a cuttingtool is not exchanged. In this manner, the adjustment of the collimatorlens 73 in the direction of the optical axis 303 can be dispensed with.

In the present embodiment, since the adjustment of the collimator lens73 in the direction of the optical axis 303 can be dispensed with, thenumber of assembling steps can be reduced and the number of parts andmechanisms for the adjustment can be decreased. Therefore, the opticalpick-up head can be small in size, light in weight and cheap in cost.Moreover, the collimator lens mounting surface 316 is flat, theadjustment of the collimator lens 73 in the x-y plane can be performed.That is to say, in case of securing the base member 311 to a pick-upchassis or a main body of a disk driver, it is necessary to bring theoptical axis 303 of the optical unit assembly to be coincided with theoptical axis of the objective lens 16 which is secured to the pick-upchassis or main body of disk driver. In this case, since the collimatorlens mounting surface 316 is a flat surface parallel with the x-y plane,the optical axis of the objective lens 16 can be positively coincidedwith the optical axis 303 oft he base member 311 by moving thecollimator lens 73 in the x-y plane by means of a pin or pins from threeor four directions. In the present embodiment, the holes 318 and 319 forsecuring the base member 311 to pick-up chassis or main body of diskdriver are formed in the base member itself, so that the number of partscan be further decreased.

FIGS. 38A, 38B and 39A, 39B show a thirteenth embodiment of the opticalpick-up head according to the invention. In the present embodiment, asurface 321 of the mounting substrate 301 of the optical unit 300parallel with the optical axis 303 of the base member 310 is urgedagainst an abutment surface 323 of a projection 322 formed in themounting portion 311 of the base member 310 so that the mountingsubstrate 301 is arranged in position in the x direction. Further thestem 88 supporting the semiconductor laser 11 is formed to extend out ofthe mounting substrate 301 and a surface 324 of the stem 88 extendingperpendicularly to the optical axis 303 is urged against a surface 325of the projection 322 of the base member 310 extending perpendicular tothe optical axis 303 to perform a positioning of the mounting substrate301 with respect to the base member 310 in the z direction. It should benoted that the surface 325 of the projection 322 and the collimator lensmounting surface 316 are parallel with each other. The remainingconstruction of the present embodiment is similar to the embodimentillustrated in FIGS. 36 and 37.

Also in the present embodiment, the distance d between the collimatorlens mounting surface 316 and the abutment surface 325 of the basemember 310 can be determined precisely, it is possible to attain similaradvantages as those of the previous embodiments shown in FIGS. 36 and37. Moreover, in the present embodiment, the distance c (see FIG. 36A)between the semiconductor laser 11 to the end surface 302 of themounting substrate 301 measured in the z direction can be determinedprecisely in a simple manner. That is, in the present embodiment, thepositioning of the base member 310 in the z direction is performed bydirectly using the surface 324 of the stem 88 having the semiconductorlaser 11 secured thereto, and thus the distance c shown in FIG. 36A doesnot relate to the distance d in FIG. 39A at all.

FIGS. 40A and 40B are plan and side views illustrating a fourteenthembodiment of the optical pick-up head according to the invention, Inthe present embodiment, the mounting substrate 301, collimator lens 73and base member 310 are constructed like as the embodiment shown inFIGS. 36 and 37 and are hermetically sealed by a cover 331. The cover331 comprises an upper portion 332 and a lower portion 333 and issecured to the flange portion 317 of the base member 310 such that themounting portion 311 of the base member 310 is surrounded by the cover331.

A plurality of electric connection pins 334 are provided on the lowerportion 333 of the cover 331 and are connected to the semiconductorlaser 11 and photodetectors 14. 18 by means of thin conductors 335. Uponproviding the cover 331, at first the lower portion 333 is secured tothe flange portion 317 and the elements 11, 14 and 18 are connected tothe pins 334 by means of the conductors 335. Then, the upper portion 332is arranged on the lower portion 333 and is secured thereto by, forinstance an adhesive agent. It is preferable that the inside of thecover 331 is filled with an inert gas such as argon and nitrogen.

In the present embodiment, the optical unit 300 is hermeticallyshielded, and thus the semiconductor laser 11, beam splitting elements12 and photodetectors 14, 18 can be effectively prevented from beingdeteriorated by dust and humidity. In this manner, it is possible toprovide the optical pick-up head having a high reliability.

In the embodiment shown in FIGS. 36 and 37, the collimator lens mountingsurface 316 and abutment surface 302 of the mounting substrate 301 areoriented in opposite directions, but according to the invention thesesurfaces may be oriented in the same direction. That is, the referenceend surface of the mounting substrate 301 is set on a left hand side ofthe mounting substrate and the abutment surface of the base member 310is provided on a left hand side of the mounting portion 311 of the basemember 310. Also in this case, the distance d between the collimatorlens mounting surface 316 and the abutment surface 314 of the basemember 310 can be determined precisely with a precision of micron order.

Furthermore, the mounting substrate 301 and base member 310 of theembodiment illustrated in FIGS. 38 and 39 may be hermetically shieldedby the cover 331 like as embodiment depicted in FIG. 40. Moreover, thesemiconductor laser 11 may be directly secured to the mounting substrate301 without using the stem 88.

What is claimed is:
 1. An optical pick-up head for reading and/orrecording information from and/or on a magneto-optical record mediumcomprising:a semiconductor laser emitting a linearly polarized lightflux; an objective lens projecting said light flux onto amagneto-optical record medium as a fine spot; a multi-image planeparallel plate arranged between said semiconductor laser and theobjective lens in a converged return light flux reflected by said recordmedium, reflecting the linearly polarized light flux emitted by saidsemiconductor laser toward said objective lens and transmitting andrefracting said return light flux to introduce astigmatism in the returnlight flux and to perform a polarizing beam splitting, said multi-imageplane parallel plate including a first triangular prism and a secondtriangular prism which are made of birefringent material and are joinedtogether; and a signal detecting photodetector receiving a plurality oflight fluxes emanating from said multi-image plane parallel plate,detecting an information signal from outputs corresponding to mutuallyorthogonally polarized light components and detecting a focusing errorsignal from outputs corresponding to ordinary and extraordinary lightcomponents; wherein said multi-image plane parallel plate is arrangedsuch that directions of major and minor axes of said astigmatism areinclined by 45 degrees with respect to a track direction in which aninformation track on the magneto-optical record medium extends, an opticaxis of said first triangular prism is set such that said return lightflux is divided into the ordinary light and extraordinary light havingsubstantially identical intensities, a polarizing film is provided on asurface of the first triangular prism upon which said linearly polarizedlight flux and return light beam are made incident, and an optic axis ofsaid second triangular prism is set to be inclined by a predeterminedangle with respect to the optic axis of the first triangular prism. 2.An optical pick-up head according to claim 1, wherein said semiconductorlaser is arranged such that a light spot formed by the objective lens onthe magneto-optical record medium becomes an elliptical shape whosemajor axis is inclined by 45 degrees with respect to the informationtrack, and a half wavelength plate is arranged between the polarizingfilm and the objective long such that a polarizing direction of thelinearly polarized light flux emitted by the semiconductor laser andimpinging upon the record medium become in parallel with the informationtrack.
 3. An optical pick-up head according to claim 1, wherein saidsemiconductor laser is arranged such that a light spot formed by theobjective lens on the magneto-optical record medium becomes anelliptical shape whose major axis is perpendicular to the informationtrack, and a first half wavelength plate is arranged between thesemiconductor laser and the polarizing film and a second half wavelengthplate is arranged between the polarizing film and the objective lenssuch that a polarizing direction of the linearly polarized light fluxemitted by the semiconductor laser and impinging upon the record mediumbecome in parallel with the information track.
 4. An optical pick-uphead according to claim 1, wherein an angle β between the optic axis ofthe first triangular prism and the optic axis of the second triangularprism measured about the optical axis of the return beam is set to45°≦β(≠90°)≦135°, said return beam is divided into a first light beamcontaining both the ordinary and extraordinary light components ofsubstantially identical intensities, and second and third light beamshaving polarizing directions which are perpendicular to each other, saidsignal detecting photodetector comprises a first light receiving unithaving four light receiving regions receiving said first light beamcontaining both the ordinary and extraordinary light components andsecond and third light receiving units receiving said second and thirdlight beams, respectively, and a focusing error signal FES is detectedfrom a difference between a sum of outputs of orthogonally aligned lightreceiving regions of the first light receiving unit and a sum of outputsof a second set of orthogonally aligned light receiving regions of thefirst light receiving unit, and an information signal is obtained from adifference between outputs of said second and third light receivingunits.
 5. An optical pick-up head according to claim 1, wherein an angleβ between the optic axis of the first triangular prism and the opticaxis of the second triangular prism measured about the optical axis ofthe return beam is set to 90°, the return beam is divided into first andsecond light beams having polarizing directions which are perpendicularto each other and emanating from the multi-image plane parallel plateseparately from each other, said signal detecting photodetectorcomprises first and second light receiving units each having four lightreceiving regions receiving respective one of said orthogonallypolarized first and second light beams, an information signal is derivedfrom a difference between a sum of the four light receiving regions ofthe first light receiving unit and a sum of the four light receivingregions of the second light receiving unit and a focusing error signalFES is detected from a sum of a first difference between a sum ofoutputs of orthogonally aligned light receiving regions of the firstlight receiving unit and a sum of outputs of a second set oforthogonally aligned light receiving regions of the first lightreceiving unit, and a second difference between a sum of orthogonallyaligned light receiving regions and a sum of orthogonally aligned lightreceiving regions of the second light receiving unit.